The present invention relates to a carburetor for combustion engines which upstream of an arbitrarily actuated throttle valve has another throttling element that is automatically controlled by a membrane unit operated by underpressure depending on the airflow. The additional throttling element controls a fuel jet by means of a needle. The discharge end of this jet is located at a point where the same underpressure prevails as in the mixing chamber formed between throttle valve and throttling element, with an enrichment system for the heating phase.
As is well known, after the starting of a cold combustion engine, continued operation requires that the mixture fed to the cold engine be enriched and the amount of mixture be increased above the amount required for the hot engine.
From German Laid-Open Document No. 14 76 155 there is known an equal-pressure carburetor where the control pressure side of the membrane (or diaphragm) unit is vented via a thermostatic needle jet during the heating phase. This results in an additional fuel quantity since the throttling element assumes a smaller opening position not corresponding to the actual air mass flow, causing the needle controlling the fuel jet to assume a different position. However, this known device does not increase the amount of mixture which is possible only with an enrichment system carrying additional fuel. Furthermore, the acceleration enrichment during the heating phase cannot be adapted to the operating condition of the engine. From the German Laid-Open Document No. 22 02 688 there is known a carburetor with an additional enrichment system for the heating phase, but this is not a system adapted to the non-stationary engine operation. The acceleration pumps usually attached to carburetors have their volume laid out for the hot engine, possibly have stepped delivery or extend the injection time, but do not permit continuous adaptation of quantity.
Accordingly, it is an object of the present invention to provide a carburetor of the previously mentioned type whose enrichment system is adapted to non-stationary engine operation, for example, which is equipped with an acceleration unit suitable for the delivery of large volumes and having compact design.
Another object of the present invention is to provide an arrangement of the foregoing character which is substantially simple in construction and may be economincally fabricated.
A further object of the present invention is to provide a carburetor, as described, which may be readily maintained in service and which has substantially long operating life.
The objects of the present invention are achieved by an enrichment system having a fuel jet controlled by a needle whose variable position is determined by the position of a temperature-sensitive element via a lever. The fuel quantity for acceleration is varied by means of a membrane unit and the system's discharge is located downstream of the throttling element. In one embodiment, the membrane unit is actuated by underpressure.
In both embodiments, the membrane unit has a pressure chamber closed by a movable membrane which is loaded by a spring. This pressure chamber has an outflow jet and the membrane operates a valve by means of a plunger.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.